The crystallography and texture of Co-based thin film deposited on Cr underlayers

Abstract

Various CO-based alloys (hcp) have been developed for use as longitudinal magnetic recording media. Many investigators have found that the use of Cr underlayers (bcc) greatly affects the magnetic properties of the films. Several investigators have related this to the effect of the Cr underlayer on the crystallographic texture of the thin magnetic CO-based films. In this review paper some of the evidence for the effect of Cr orientation on the crystallographic orientation of CO-based thin films is presented. This evidence is based on x-ray diffraction, selected area electron diffraction, electron micro-diffraction of the Co/Cr bi-layer film and atomic resolution electron microscopy of cross sections of the bi-lay9 films. We show that a (110) Cr surface gives rise to a (1011) type CO-based alloy thin film texture, whereas a (200) Cr surface produces a ( 1120) type CO-based alloy thin fiim texture.It has been nearly a quarter of a century since the discovery that a Cr underlayer increases the in-plane magnetic coercivity of sputtered CO based alloy thin films [1,2]. One of the proposed mechanisms for this increase in coercivity is the supposition that the Cr underlayer produces a CO film with a preferred crystallographic orientation [3,4]. In a previous paper we reviewed some of the evidence for crystallographic texture in these thin films [5]. In this paper we review four experimental techniques that can be used to investigate the orientation relationships (OR) between the magnetic Cobased film and the Cr underlayer. These techniques are x-ray diffraction, selected area (electron) diffraction (SAD), electron microdiffraction (ID) and atomic resolution electron microscopy. Figure 1 is a schematic drawing showing the important components of a thin film disk for magnetic recording. Of interest to us in this review is the crystallographic orientation relationships between the grains in the magnetic film and those in the Cr (bcc) underlayer. The magnetic films which we discuss will all be alloys of CO, usually with the hcp structure. Hence, the ORs of interest to us are those between hcp and bcc. Since certain interplanar spacings in CO and Cr have nearly the same values, a special set of ORs are established during the deposition process of the CO-based alloy onto the Cr underlayer. The govemment has certain rights in this material. I NiP (amorphous) 10 p I Figure 1. A schematic drawing of the various layer in a hard disk We start with a brief review of the important planes in the bcc and hcp structures. Figure 2(a) shows the two types of planes of Cr which are most likely to be parallel to the thin film surface, namely the (200) and (110) planes. The (110) planes are the closest-packed planes for the bcc structure, and in the case of Cr films are the ones which are most likely to lie parallel to the film surface when the films are grown without substrate heating [6]. When deposited at elevated temperatures (>15OoC) the (200) texture is commonly observed [7-lo]. The figures shown in 2(b) highlight the hexagonal close pa...

Development of microstructure in Cr and Cr/CoCrPt films made by pulsed laser deposition

“…1 The grain size and crystallographic orientation of the Cr layer govern the structure and magnetic properties of the Co-alloy overlayer [2][3][4] and, ultimately, the recording performance of the disk. A ͕100͖ preferred orientation in the Cr, which leads to an epitaxial ͕112 0͖ Co-alloy preferred orientation, is desirable because it creates an in-plane orientation of the c axis ͑the magnetic easy axis͒ of the Co-alloy layer.…”

Effect of the underlayer on the microstructure and surface evolution in Al-0.5wt.%Cu polycrystalline thin films

“…Details on how the 1DPSD spectra were obtained are provided elsewhere. 16 The scaling exponent a may be determined 17 from the 1DPSD spectra, because a self-affine structure exhibits a power-law decay in a finite frequency range (4) where K 0 is a constant dependent on the system and ␥ is related to the scaling exponent by ␣ ϭ (␥ Ϫ d)/2, 18 where the line scan dimension d ϭ 1. The growth exponent ␤ is evaluated from Eq.…”

“…2 Examples of extreme substrate control include the heteroepitaxial growth of a single-crystal film above a single-crystal substrate 3 and the growth of a polycrystalline film with a grain-to-grain heteroepitaxial relationship with a polycrystalline substrate. 4 At the other extreme, a noninteracting film and substrate combination is one in which the substrate provides only a suitable surface for deposition and growth. Even in this case, however, energy minimization driving forces may lead to preferred orientation of the depositing film.…”

Effect of underlayer thickness on magnetic properties of SmCo film

“…[1][2][3][4] The reason why the Cr underlayer is used for the SmCo layer is because it provides a close epitaxial match to the planes of hexagonal-close-packed ͑hcp͒ Co-alloy films and promotes in-plane orientation of the c axis of hexagonal Co-alloy films. 5 Liu et al investigated the epitaxial relation between the SmCo crystallite and the crystal structure of the Cr underlayer using a high resolution electron microscopy ͑HREM͒ and obtained the lattice constant of each crystallite. They obtained the lattice constants of aϭ0.289 nm for Cr crystallites, and aϭ0.253 and cϭ0.413 nm for SmCo crystallites, respectively.…”